Line a 9×9 or 8×8-inch baking pan with parchment paper, ensuring the edges extend over the sides for easy removal of the caramels later. Set aside.

In a heavy-bottomed 3-quart saucepan, combine the butter, brown sugar, corn syrup, sweetened condensed milk, Fireball whiskey, and salt.

Bring the mixture to a boil over medium heat. Cook without stirring until the candy thermometer registers 246°F (firm ball stage), about 10 to 15 minutes.

The mixture will darken as it cooks; if using a stainless steel pan, keep heat moderate and swirl occasionally to avoid burning.

Once at the right temperature, remove the pan promptly from heat. Stir in the vanilla extract until fully incorporated and smooth.

Immediately pour the hot caramel into the prepared pan and smooth the surface with a spatula or the back of a spoon.

Allow the caramel to cool undisturbed at room temperature for 2 to 4 hours until fully set and firm to the touch.

Once cooled, lightly mark the caramel with a ruler then cut into one-inch squares using a buttered knife.

Wrap each piece in wax paper to prevent sticking.

Store at room temperature in an airtight container for up to two weeks.